Methods of forming metal oxide

ABSTRACT

Some embodiments include methods of forming memory cells. Metal oxide may be deposited over a first electrode, with the deposited metal oxide having a relatively low degree of crystallinity. The degree of crystallinity within the metal oxide may be increased after the deposition of the metal oxide. A dielectric material may be formed over the metal oxide, and a second electrode may be formed over the dielectric material. The degree of crystallinity may be increased with a thermal treatment. The thermal treatment may be conducted before, during, and/or after formation of the dielectric material.

TECHNICAL FIELD

Methods of forming metal oxide and memory cells.

BACKGROUND

Memory is one type of integrated circuitry, and may be used in computersystems for storing data. Integrated memory is usually fabricated in oneor more arrays of individual memory cells. The memory cells areconfigured to retain or store memory in at least two differentselectable states. In a binary system, the states are considered aseither a “0” or a “1”. In other systems, at least some individual memorycells may be configured to store more than two levels or states ofinformation.

There is a developing interest in memory cells which have programmablematerial provided between a pair of electrically conductive electrodes.Such memory cells may be referred to as cross-point memory cells.

Programmable materials suitable for utilization in cross-point memorywill have two or more selectable and electrically differentiable memorystates. The multiple selectable memory states can enable storing ofinformation by an individual memory cell. The reading of the cellcomprises determination of which of the memory states the programmablematerial is in, and the writing of information to the cell comprisesplacing the programmable material in a predetermined memory state.

Some memory cells utilize multiple discrete materials between theelectrodes to create the programmable material. Such memory cells may beprogrammed by moving oxygen species (for instance, oxygen ions) withinand/or between the materials. Memory devices that utilize migration ofmobile charge carriers to transition from one memory state to anotherare sometimes referred to as Resistive Random Access Memory (RRAM)cells.

At least one of the materials utilized in such RRAM may be a conductivemetal oxide (for instance, a combination of Pr, Ca, Mn and O; which iscommonly referred to as PCMO). It can be difficult to consistently formmetal oxide having uniform desired characteristics (for instance, highconductivity) across an array of memory cells.

Accordingly, it is desired to develop new methods for forming conductivemetal oxide within RRAM cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 are diagrammatic cross-sectional views of a portion of aconstruction at various stages of an example embodiment process offorming a memory cell.

FIGS. 6-8 are diagrammatic cross-sectional views of a portion of aconstruction at various stages of another example embodiment process offorming a memory cell. The process stage of FIG. 6 follows that of FIG.2.

FIG. 9 is a flow chart diagram illustrating process flows of someexample embodiments.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Metal oxides (such as, for example, PCMO) may have amorphous andcrystalline states. The crystalline states may have improved electricalproperties for utilization in RRAM relative to the amorphous states; andmay, for example, have lower resistance, improved oxygen ion migration,etc. Conventional methods deposit conductive metal oxide in crystallineform during fabrication of RRAM. However, such methods are slow (withdeposition rates typically being less than or equal to about 0.3Å/second), and thus negatively impact desired throughput of afabrication process.

Some embodiments include recognition that various metal oxides may betransformed from an amorphous form into a crystalline form by reducingthe oxygen content of the metal oxides. Thus, metal oxides may bedeposited in an amorphous form at a relatively high deposition rate (forinstance, greater than or equal to about 2 Å/second), and then convertedinto crystalline form by reducing the oxygen content of the metaloxides. A possible mechanism relative to PCMO is that a higher oxidationof manganese promotes an amorphous phase with higher resistance, while alower oxidation of manganese promotes a crystalline phase with lowerresistance. The terms “higher oxidation” and “lower oxidation” arerelative to one another, rather than having meaning relative to anexternal scale. Thus, the “higher oxidation” is a higher oxidation thenthe “lower oxidation,” and may or may not correspond to one of thehighest oxidation states of manganese. Similarly, the terms “higherresistance” and “lower resistance” are relative to one another ratherthan having meaning relative to external scale. Thus, the “lowerresistance” is a lower resistance than the “higher resistance,” and mayor may not correspond to a lowest resistance state of the metal oxide.

The oxygen content within the metal oxide may be reduced with anysuitable method. In some embodiments, the oxygen content of the metaloxide may be reduced by maintaining the metal oxide at a temperature ofat least about 600° C. for a duration of at least about 5 minutes whileexposing the metal oxide to an environment which is either inertrelative to reaction with all constituents of the metal oxide, orreducing relative to reaction with one or more constituents of the metaloxide. Example embodiments are discussed below with reference to FIGS.1-9.

Referring to FIG. 1, a construction 10 is shown to comprise an electrodematerial 14 over a base 12.

The base 12 may be a semiconductor base; and may comprise, consistessentially of or consist of monocrystalline silicon. If the basecomprises semiconductor material, it may be referred to as asemiconductor substrate, or as a portion of a semiconductor substrate.The terms “semiconductive substrate,” “semiconductor construction” and“semiconductor substrate” mean any construction comprisingsemiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials), and semiconductive materiallayers (either alone or in assemblies comprising other materials). Theterm “substrate” refers to any supporting structure, including, but notlimited to, the semiconductive substrates described above. Although base12 is shown to be homogenous, the base may comprise numerous materialsin some embodiments. For instance, base 12 may correspond to asemiconductor substrate containing one or more materials associated withintegrated circuit fabrication. In such embodiments, such materials maycorrespond to one or more of refractory metal materials, barriermaterials, diffusion materials, insulator materials, etc.

The electrode material 14 may comprise any suitable electricallyconductive composition or combination of compositions; and in someembodiments may comprise, consist essentially of, or consist ofplatinum. The electrode material may be formed to any suitablethickness, and in some embodiments may be formed to a thickness of atleast about 1000 angstroms (such as, for example, a thickness of about2000 angstroms). The electrode material 14 forms a first electrode 15.

Referring to FIG. 2, metal oxide 16 is deposited over the firstelectrode 15. The metal oxide may comprise any suitable composition orcombination of compositions; and in some embodiments may comprise,consist essentially of, or consist of oxygen in combination with one ormore of praseodymium, barium, calcium, manganese, strontium, titanium,iron, cesium and lead. For instance, the metal oxide may comprise,consist essentially of, or consist of PCMO; or more specifically maycomprise, consist essentially of, or consist of PrCaMnO, where thelisted composition is described in terms of principle components ratherthan in terms of a specific stoichiometry.

The deposition of the metal oxide may utilize any suitable methodology,including, for example, one or more of physical vapor deposition (PVD),atomic layer deposition (ALD) and chemical vapor deposition (CVD).

The metal oxide 16 is deposited with a relatively low degree ofcrystallinity (with the term “relatively low” indicating that thecrystallinity is low relative to another degree of crystallinity thatwill ultimately be induced at a subsequent processing stage), and insome embodiments the deposited metal oxide may be entirely amorphous.The metal oxide 16 may be considered to be a low degree of crystallinityform of the metal oxide.

Referring to FIG. 3, the metal oxide is subjected to treatment whichincreases the degree of crystallinity of the metal oxide and thustransforms the metal oxide into a metal oxide 18 having a high degree ofcrystallinity. The metal oxide 18 has a higher degree of crystallinitythan the metal oxide 16 (FIG. 2), and in some embodiments the metaloxide 18 may be entirely crystalline. The high degree of crystallinityform of the metal oxide may have increased electrical conductivity(i.e., lowered electrical resistance) relative to the low degree ofcrystallinity form of the metal oxide, and in some embodiments the metaloxide 18 may be electrically conductive while the metal oxide 16 is not.

The processing utilized to increase the degree of crystallinity of themetal oxide in transitioning from the process stage of FIG. 2 to that ofFIG. 3 may comprise a thermal treatment of the metal oxide coupled withexposure of the metal oxide to an environment which is either inertrelative to reaction with all constituents of the metal oxide orreducing relative to reaction with one or more constituents of the metaloxide.

The thermal treatment may comprise an anneal that maintains atemperature of the metal oxide at a temperature of at least about 600°C. for a duration of several minutes (for instance, a duration of atleast about 5 minutes).

If a reducing environment is utilized during such anneal, theenvironment may comprise H₂. The H₂ may increase crystallinity withinthe metal oxide by, for example, reacting with oxygen to form water andthus drive an equilibrium toward depletion of oxygen from the metaloxide. Additionally, or alternatively, the hydrogen may stabilize alower oxidation state of the metal oxide by interacting with danglingbonds to chemically passivate the dangling bonds.

If an inert environment is utilized during the anneal of the metaloxide, the environment may comprise, consist essentially of, or consistof N₂, argon, and/or other gases which are inert relative to reactionwith all constituents of the metal oxide at the temperatures utilizedduring the thermal treatment.

The metal oxide 18 may be formed to any suitable thickness; and in someembodiments may be formed to a thickness greater than or equal to about50 Å, such as, for example, a thickness of about 350 Å.

Referring to FIG. 4, dielectric material 20 can be deposited over metaloxide 18. The deposition may comprise any suitable methodology,including for example, one or both of ALD and CVD.

The dielectric material may comprise any suitable composition orcombination of compositions; and in some embodiments may comprise one ormore of metal oxide, silicon dioxide and silicon nitride. If thedielectric material 20 comprises metal oxide, the dielectric materialmay be referred to as a second metal oxide to distinguish it from thefirst metal oxide 18. In some embodiments, dielectric material 20 maycomprise, consist essentially of, or consist of one or both of hafniumoxide and zirconium oxide. In such embodiments, the oxide of dielectricmaterial 20 may be formed utilizing a relatively mild oxidant (such as,for example, water) in order to avoid inadvertently oxidizing theconductive metal oxide 18. For instance, in some embodiments thedielectric material 20 may consist of one or both of hafnium oxide andzirconium oxide, and may be formed utilizing water as the only source ofoxygen within the dielectric material.

The dielectric material 20 may be formed to any suitable thickness, andin some embodiments may be formed to a thickness of less than or equalto about 50 Å; such as, for example, a thickness of less than or equalto about 30 Å.

Referring to FIG. 5, electrode material 22 is formed over dielectricmaterial 20. The electrode material 22 may comprise any suitablecomposition or combination of compositions, and may comprise anidentical composition as electrode material 14 or a differentcomposition from electrode material 14. In some embodiments, electrodematerial 22 may comprise, consist essentially of, or consist ofplatinum, either alone, or in combination with metal silicide (forinstance, tungsten silicide).

The electrode material 22 forms an electrode 23. In some embodiments,the electrodes 15 and 23 may be referred to as a first electrode and asecond electrode, respectively, to distinguish such electrodes from oneanother.

The electrodes 15 and 23, together with the materials 18 and 20, form amemory cell 28.

The electrode 15 is shown connected to circuitry 24, and the electrode22 is shown connected to circuitry 26. In operation, the circuitries 24and 26 are utilized to provide voltage between the electrodes 15 and 23.The voltage may be utilized for erasing the memory cell, programming thememory cell and/or for determining resistance across the memory cell andthereby reading a memory state of the memory cell.

The memory cell 28 is an RRAM cell. Such RRAM cell may be programmed bymoving oxygen species (for instance, oxygen ions) within and/or betweenthe materials 18 and 20. For instance, if the dielectric material 20comprises a metal oxide, such dielectric material may be referred to asan inter-metal oxide (IMO), and programming of the RRAM cell maycomprise oxygen diffusion from the conductive metal oxide 18 into theIMO (and possibly to an interface of the IMO with the second electrode23) under an appropriate voltage.

The processing of FIGS. 1-5 converts metal oxide from the low degree ofcrystallinity form of the metal oxide (the metal oxide 16 of FIG. 2) tothe high degree of crystallinity form of the metal oxide (the metaloxide 18 of FIG. 3) prior to deposition of the dielectric material 20(FIG. 4). In other embodiments, such conversion from the low degree ofcrystallinity form to the high degree of crystallinity form may occur,at least in part, during and/or after formation of the dielectricmaterial 20. FIGS. 6-8 illustrate an example process in which theconversion from the low degree of crystallinity form to the high degreeof crystallinity form occurs after formation of the dielectric material.Similar numbering will be utilized to describe FIGS. 6-8 as is utilizedabove to describe FIGS. 1-5, where appropriate.

Referring to FIG. 6, a construction 10 a is shown at a processing stagesubsequent to that of FIG. 2. The construction 10 a comprises thedielectric material 20 formed over the low degree of crystallinity formof the metal oxide (i.e., the metal oxide 16).

Referring to FIG. 7, the construction 10 a is shown after it has beensubjected to processing suitable to convert the metal oxide from the lowdegree of crystallinity form of the metal oxide (the metal oxide 16 ofFIG. 6) to a high degree of crystallinity form of the metal oxide (themetal oxide 18 of FIG. 7). Such processing may be analogous to theprocessing discussed above with reference to FIG. 3. The dielectricmaterial 20 utilized in the processing of FIGS. 6 and 7 should be thinenough and of suitable composition so that oxygen may migrate out of theunderlying metal oxide and either into or through the dielectricmaterial 20 so that the metal oxide may be converted from the low degreeof crystallinity form to the high degree of crystallinity form. In someembodiments, dielectric material 20 may have a thickness of less than orequal to about 50 Å; such as, for example, a thickness of less than orequal to about 30 Å.

An advantage of the processing of FIGS. 6 and 7 may be that thedielectric material 20 can be formed utilizing a more aggressive oxidantthan can be utilized during above-discussed process stage of FIG. 4.Specifically, since the process stage of FIG. 4 followed the removal ofoxygen from the metal oxide to convert the metal oxide from the lowdegree of crystallinity form to the high degree of crystallinity form,the dielectric material 20 was formed under conditions which would notre-introduce oxygen into the metal oxide 18. In contrast, the processingof FIGS. 6 and 7 converts the metal oxide from the low degree ofcrystallinity form to the high degree of crystallinity form afterformation of the dielectric material. Thus, it may not be problematicfor oxygen to be introduced into the metal oxide during formation of thedielectric material since such oxygen can be subsequently removed afterformation of the dielectric material. Accordingly, ozone or otheraggressive oxidant may be utilized during formation of the dielectricmaterial 20 shown at the processing stage of FIG. 6. For instance,dielectric material 20 may comprise hafnium oxide and/or zirconium oxideformed utilizing ozone as the source of oxygen within such dielectricmaterial.

FIG. 8 shows construction 10 at a processing stage analogous to thatdiscussed above with reference to FIG. 5, and shows that the variousmaterials may be incorporated into an RRAM cell 28 identical to thatdiscussed above with reference to FIG. 5.

Various embodiments may comprise one or more process stages utilized toremove oxygen from metal oxide to increase crystallinity and/or decreaseelectrical resistance within the metal oxide, and such process stagesmay occur before, during and/or after formation of dielectric materialover the metal oxide. Thus, the processing discussed above withreference to FIGS. 1-5 may be utilized in combination with theprocessing discussed with reference to FIGS. 6-8 in some embodiments.

FIG. 9 shows a flowchart illustrating some process sequences that may beutilized in some embodiments.

At an initial stage 40, a first electrode is formed. Such electrode maybe analogous to the electrode 15 of FIG. 1.

At a subsequent stage 42, metal oxide is formed over the firstelectrode, with the metal oxide having a first degree of crystallinity.Such metal oxide may be analogous to the metal oxide 16 shown in FIG. 2.

The metal oxide may then be thermally treated as shown at stage 44 toincrease the degree of crystallinity, and dielectric material may beformed over the metal oxide as shown at stage 46. The metal oxide havingthe increased crystallinity may be analogous to the oxide 18 of FIG. 3,and the dielectric material may be analogous to the dielectric material20 of FIG. 4.

After the dielectric material is formed, the metal oxide may bethermally treated to increase the degree of crystallinity as shown atthe stage 48, and the second electrode may be formed over the dielectricmaterial as shown at a stage 50. The second electrode may be analogousto the electrode 23 of FIG. 5.

The flowchart of FIG. 9 shows that some embodiments thermally treat themetal oxide prior to forming the dielectric material (i.e., flow tostage 44 and then to stage 46), while other embodiments form thedielectric material without first thermally treating the metal oxide(i.e., flow directly from stage 42 to stage 46). The flowchart of FIG. 9also shows that some embodiments thermally treat the metal oxide afterforming the dielectric (i.e., flow from stage 46 to stage 48), whileother embodiments form the second electrode over the dielectric materialimmediately after forming the dielectric material (i.e., flow from stage46 directly to stage 50). Thus, the invention includes embodiments inwhich metal oxide is thermally treated only prior to forming dielectricmaterial, embodiments in which metal oxide is thermally treated onlyafter forming dielectric material, and embodiments in which metal oxideis thermally treated both prior to forming dielectric material and afterforming dielectric material. Further, the invention includes embodimentsin which the metal oxide is thermally treated during formation of thedielectric material (not shown in FIG. 9).

RRAM cells formed in accordance with the methods discussed above may beincorporated into memory arrays or other integrated circuitry. Suchintegrated circuitry may be incorporated into electronic systems. Suchelectronic systems may be any of a broad range of systems, such as, forexample, clocks, televisions, cell phones, personal computers,automobiles, industrial control systems, aircraft, etc.

The particular orientation of the various embodiments in the drawings isfor illustrative purposes only, and the embodiments may be rotatedrelative to the shown orientations in some applications. The descriptionprovided herein, and the claims that follow, pertain to any structuresthat have the described relationships between various features,regardless of whether the structures are in the particular orientationof the drawings, or are rotated relative to such orientation.

The cross-sectional views of the accompanying illustrations only showfeatures within the planes of the cross-sections, and do not showmaterials behind the planes of the cross-sections in order to simplifythe drawings.

When a structure is referred to above as being “on” or “against” anotherstructure, it can be directly on the other structure or interveningstructures may also be present. In contrast, when a structure isreferred to as being “directly on” or “directly against” anotherstructure, there are no intervening structures present. When a structureis referred to as being “connected” or “coupled” to another structure,it can be directly connected or coupled to the other structure, orintervening structures may be present. In contrast, when a structure isreferred to as being “directly connected” or “directly coupled” toanother structure, there are no intervening structures present.

Some embodiments include a method of increasing crystallinity within ametal oxide. The method includes annealing the metal oxide at atemperature of at least about 600° C. while exposing the metal oxide toan environment which is either inert relative to reaction with allconstituents of the metal oxide, or reducing relative to reaction withone or more constituents of the metal oxide. The metal oxide iselectrically conductive after the anneal.

Some embodiments include a method of forming an electrically conductivemetal oxide. Metal oxide is deposited over an underlying material. Afterthe metal oxide is deposited, crystallinity of the metal oxide isincreased by annealing the metal oxide at a temperature of at leastabout 600° C. while exposing the metal oxide to an environment which isreducing relative to reaction with one or more constituents of the metaloxide.

Some embodiments include a method of forming a memory cell. Metal oxideis deposited over a first electrode, with the deposited metal oxidehaving a relatively low degree of crystallinity. After the metal oxideis deposited, the degree of crystallinity within the metal oxide isincreased. The metal oxide having the increased degree of crystallinityis electrically conductive. A dielectric material is formed over themetal oxide, and a second electrode is formed over the dielectricmaterial.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

I/we claim,:
 1. A method of increasing crystallinity within a metaloxide, comprising: annealing the metal oxide at a temperature of atleast about 600° C. while exposing the metal oxide to an environmentwhich is either inert relative to reaction with all constituents of themetal oxide, or reducing relative to reaction with one or moreconstituents of the metal oxide; the metal oxide being electricallyconductive after said anneal.
 2. The method of claim 1 wherein the metaloxide comprises oxygen in combination with one or more of praseodymium,barium, calcium, manganese, strontium, titanium, iron, cesium and lead.3. The method of claim 1 wherein the metal oxide comprises PrCaMnO;where the listed composition is described in terms of principlecomponents, rather than in terms of a specific stoichiometry.
 4. Themethod of claim 1 wherein the environment comprises H₂.
 5. The method ofclaim 1 wherein the environment comprises argon and/or N₂.
 6. A methodof forming an electrically conductive metal oxide, comprising:depositing metal oxide over an underlying material; and after thedepositing, increasing crystallinity of the metal oxide by annealing themetal oxide at a temperature of at least about 600° C. while exposingthe metal oxide to an environment which is reducing relative to reactionwith one or more constituents of the metal oxide.
 7. The method of claim6 wherein the metal oxide comprises PrCaMnO, where the listedcomposition is described in terms of principle components, rather thanin terms of a specific stoichiometry; wherein the deposited metal oxideis entirely amorphous; and wherein the environment comprises H₂.
 8. Amethod of forming a memory cell, comprising: depositing metal oxide overa first electrode, the deposited metal oxide having a relatively lowdegree of crystallinity; after the depositing, increasing the degree ofcrystallinity within the metal oxide, the metal oxide having theincreased degree of crystallinity being electrically conductive; forminga dielectric material over the metal oxide; and forming a secondelectrode over the dielectric material.
 9. The method of claim 8 whereinthe increasing the degree of crystallinity comprises a thermal treatmentof the metal oxide conducted prior to formation of the dielectricmaterial.
 10. The method of claim 9 wherein the metal oxide is a firstmetal oxide, and wherein the dielectric material comprises a secondmetal oxide, and wherein the formation of the dielectric materialutilizes water as the only source of oxygen for the second metal oxide.11. The method of claim 10 wherein the second metal oxide consists ofone or both of hafnium oxide and zirconium oxide.
 12. The method ofclaim 8 wherein the increasing the degree of crystallinity comprises athermal treatment of the metal oxide conducted after formation of thedielectric material.
 13. The method of claim 8 wherein the increasingthe degree of crystallinity comprises a thermal treatment of the metaloxide conducted during formation of the dielectric material.
 14. Themethod of claim 8 wherein the increasing the degree of crystallinitycomprises: a first thermal treatment of the metal oxide conducted priorto formation of the dielectric material; and a second thermal treatmentof the metal oxide conducted during and/or after formation of thedielectric material.
 15. The method of claim 14 wherein the first andsecond thermal treatments each comprise maintaining the metal oxide at atemperature of at least about 600° C. for a duration of at least about 5minutes.
 16. The method of claim 8 wherein the deposited metal oxide isentirely amorphous.
 17. The method of claim 8 wherein the increasing thedegree of crystallinity comprises annealing the metal oxide at atemperature of at least about 600° C. while exposing the metal oxide toan environment which is either inert relative to reaction with allconstituents of the metal oxide, or reducing relative to reaction withone or more constituents of the metal oxide.
 18. The method of claim 17wherein the anneal is conducted before formation of the dielectricmaterial.
 19. The method of claim 17 wherein the anneal is conductedduring formation of the dielectric material.
 20. The method of claim 17wherein the anneal is conducted after formation of the dielectricmaterial.
 21. The method of claim 8 wherein the metal oxide comprisesoxygen in combination with one or more of praseodymium, barium, calcium,manganese, strontium, titanium, iron, cesium and lead.
 22. The method ofclaim 8 wherein the metal oxide is a first metal oxide, and wherein thedielectric material comprises one or more of a second metal oxide,silicon dioxide and silicon nitride.
 23. The method of claim 22 whereinthe dielectric material is formed to a thickness of less than or equalto about 50 Å.